The investigators propose to continue their consortium of population-based case-control studies to 1) investigate the relation between postmenopausal hormone therapy and breast cancer mortality, and 2) evaluate the relation between certain lifestyle factors, including weight change, physical activity, pregnancy termination, and breast cancer incidence. (As in the past, Wisconsin, Harvard, and Dartmouth will have submitted separate applications with identical research plans.) Several studies have suggested improved survival among women using estrogen preparations at the time of breast cancer diagnosis. The investigators will evaluate the relation between postmenopausal hormone therapy and breast cancer mortality, ascertained though state vital records and the National Death Index, among cases enrolled in our previous and ongoing collaborative breast cancer studies in Wisconsin, Massachusetts, and New Hampshire (1988-95). Of the nearly 13,000 cases enrolled, they estimate that a minimum of 2600 deaths will have occurred in postmenopausal women. Thus, they will have ample power to evaluate the effects of postmenopausal hormone therapy, and to assess potential interactions with alcohol use and obesity, which may influence endogenous hormone levels. In addition, the availability of extensive questionnaire information will allow exploration of the possible effects of other exposures, including smoking and dietary factors, on breast cancer mortality. To meet their second aim, they will enroll 9000 breast cancer cases aged 20-69 and a comparable number of controls in our respective states over a 3-year period. Cases will be identified through state tumor registries, and controls through state drivers license lists and Medicare beneficiary lists. The large sample size is necessary to evaluate study hypotheses since the associations of interest are modest and patterns of exposure infrequent, e.g., weight gain at specific ages and induced abortions prior to full term pregnancies. The investigators state that the proposed studies, based on an efficient, well-established mechanism for selecting and interviewing cases and controls, and analysis of existing population-based data on thousands of women with breast cancer, will provide timely new information on potentially modifiable lifestyle determinants of breast cancer incidence and survival, in a highly cost- effective manner.